11 ACPI Sleeping StatesAdvanced Configuration and Power Interface (ACPI)OS-directed configuration; Power/thermal managementGlobal System StatesG0 --- Working (System Operational)G1---Sleeping (CPU stopped)G2 ---Soft OffG3 ---Mechanical off (Physical off switch)Sleeping States in G1: S0 – S5S3: also called Standby, Suspend to RAMDRAM still maintainedS4: also called Hibernation or Suspend to DiskDRAM not maintainedDevice Power States: D0 – D3D0 - Fully-OnD3 -- Power off to device

12 Attack Model Assumption Attacks from the untrusted OS Out of the scopeBIOS and option ROM on devices can be trusted.No physical access to the protected machineAttacks from the untrusted OSSpoofing Trusted OS attacks: faking trusted OSData exfiltration attacks: stealing sensitive dataCache-based side channel attacks: extracting sensitive dataOut of the scopeDenial of Service attacksNetwork attacks on trusted OS

14 Trusted PathProtect against Spoofing trusted OS attacks by assuring users that they are working with the OS they intend to use.Protecting system variablesOS_Flag: records which OS should be woken nextWhere to save it?Untrusted OS should be truly suspended.hardware controlled power LED lights up when system is powered on, and blinks in the sleep mode.BIOS should be entered.Press the power button.OS_Flag: physical jumper, e.g., Parallel port connector

17 DIMM Mask and DQS SettingMemory IsolationA motherboard may have more than one dual in-line memory module (DIMM) slot.DIMM Mask and DQS SettingBIOS uses “DIMM_MASK”variable to control which DIMMs to be enabled.BIOS sets “data strobes”(DQS) parameters to enable DDR RAM memory access.

18 Memory Isolation Physical-level memory isolation ensured by BIOSTwo OS environments run in separate DIMMS.BIOS only enables one DIMM for each OS.Two DQS settings for two OSes“DIMM_MASK” controlled by the physical jumper.System software, except the BIOS, cannot initialize or enable DIMMs after the system boots upTransient state of DQS settingIf “DIMM_MASK”has conflicts with DQS setting, system crashes